Electrophotography is extensively used and applied in recent years not only in the field of copiers but in the field of various printers because of its instantaneousness, ability to give high-quality images, etc. With respect to photoreceptors serving as the core of electrophotography, organic photoreceptors have been developed which employ an organic photoconductive material having advantages over inorganic photoconductive materials, such as pollution-free nature and ease of production. Although an organic photoreceptor generally comprises a conductive support and a photosensitive layer formed thereon, known examples thereof include photoreceptors of the so-called single-layer type which have a single-layer photosensitive layer comprising a binder resin and a photoconductive material dissolved or dispersed therein and photoreceptors of the so-called lamination type which have a photosensitive layer composed of superposed layers comprising a charge-generating layer containing a charge-generating material and a charge-transporting layer containing a charge-transporting material.
The layer possessed by an organic photoreceptor is generally formed by applying and drying a coating fluid prepared by dissolving or dispersing materials in any of various solvents because this method has high productivity. However, in the case of the charge-generating layer comprising a charge-generating material and a binder resin, the charge-generating material and the binder resin in the charge-generating layer are present in the state of being incompatible with each other. Because of this, the charge-generating layer formation coating fluid is formed by applying a coating fluid containing the charge-generating material dispersed therein.
Hitherto, such a coating fluid has been produced by subjecting a charge-generating material to a long-term wet dispersing treatment in an organic solvent with a known mechanical pulverizer such as a ball mill, sand grinding mill, planetary mill, or roll mill (see, for example, patent document 1).
It has been proposed that in the case of dispersing the charge-generating material in a coating fluid for charge-generating-layer formation with a dispersing medium, use of a glass or zirconia as the material of the dispersing medium enables an electrophotographic photoreceptor having excellent electrical properties to be provided (see, for example, patent document 2).    Patent Document 1: JP-A-2001-290292    Patent Document 2: JP-A-2004-78140